1. Field of the Invention
The present invention relates to an imaging device, an image system and an imaging method.
2. Description of the Related Art
Conventionally, a device that handles video signals uses an image correction processing circuit which carries our proper signal processing on a video signal and thus provides a desired output video. For example, in the case where visibility of the video signal is lowered by the influence of fog, yellow sand, haze or the like, there is a technique of correcting the image and improving visibility via image correction processing.
FIG. 9 shows an image scene where there is no fog or the like. As a video signal histogram of the entire image in this case, a histogram in which video signals are distributed from the dark side to the bright side as shown in FIG. 10 is obtained.
Meanwhile, with respect to a scene where there is fog or the like as shown in FIG. 11, a histogram having a smaller signal range than the video signal histogram without fog or the like is obtained. When, an image is outputted based on the histogram with the smaller signal range, a video with lower visibility is provided because of lower contrast. The reference symbols det_d, det_l and width will be described later in an embodiment of the invention.
JP-A-2010-147969 is a background art to improve the lowered visibility of the image due to fog or the like.
JP-A-2010-147969 discloses that “an image correction processing circuit according to the invention comprises: an image correction unit which carries out predetermined image correction processing on an input image and generates an output image; an arithmetic unit which acquires a luminance histogram for each field of the input image and calculates two values or all three values of an average luminance value, a standard, deviation value and an intermediate value of the luminance histogram; and a correction control unit which determines whether image correction processing on the input image is needed or not and an amount of correction, based on the two values or all the three values of the average luminance value, the standard deviation value and the intermediate value of the luminance histogram calculated by the arithmetic unit, and controls the image correction unit.”
In the related art, the average luminance value, the standard deviation value and the intermediate value with respect to the video signal of the entire image are used to determine whether there is fog, yellow sand, base or the like, and whether image correction processing needs to be applied to the input image or not and the amount of correction are determined.
By the way, an input image may partly include an object appearing with high luminance due to light or the like, or an object appearing with low luminance due to shadow or the like, in addition to fog. FIG. 13 shows an input image or such a scene. FIG. 14 shows a video signal histogram of the entire input image of FIG. 13. The video signal histogram shown in FIG. 14 includes both a video signal histogram with a small signal range due to the influence of fog or the like as shown in FIG. 12 and histograms on the dark side and the bright side due to the influence of the high luminance and the low luminance.
If the related art is used in such a case, fog determination and decision on the amount of correction are carried out using the histogram of the entire image and therefore the average luminance value, the standard deviation value and the intermediate value of the video signal histogram of the entire image change largely, influenced by the histograms on the dark side and the bright side due to the high luminance and the low luminance. Therefore, despite being a foggy scene, the image can be determined as not being a foggy scene and vice versa. This causes a significant fall in foggy scene discrimination accuracy. In such cases, image processing is carried out even when there is no need to carry out correction processing, and an increase in noise due to the correction processing or the like occurs.